This PPT intends to explore the beauty of the secondary cell wall thickenings with special reference to adcrustation, incrustation & transport cells.

1. Cell Wall ingrowths: Adcrustation &
Incrustation
By
N.Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia, 723101(W.B) India

2.  Adcrustation is the process of addition of any
substance particularly the secondary materials from
inside the whole substance .It means that nothing is
added on the surface of the body to make the
substances thick or big , rather the growth comes
from the whole body. The growth of the fruits is an
ideal example.
 Incrustation , on the other hand, is the process by
which the substances grow with the addition of new
layers on the surface of the body. The cell wall of the
plants grow by the process of incrustation.

3.  When certain organic molecules penetrate the primary wall
and undergoes polymer formation, the cell wall undergoes
incrustation.
 Lignin is the most important incrusting substances and it is
insoluble constituent of the cell wall, aromatic and of high
molecular weight. It is synthesized by the oxidative
polymerization of monolignols like coumaryl, coniferyl and
sinapyl alcohols-the products of phenylpropane pathway.
 During the incrustation of the cell wall with lignin, the more
hydrophilic matrix sinks and is compressed by the
displacement of water. It occurs predominantly in the region of
the middle lamellae. Incrustation with lignin decreases the
water permeability of the wall and the lignin deposits add
mechanical strength.

4.  It is the process in which the outer walls of the epidermis of
leaves and other aerial regions, the walls of cork cells, certain
walls of inner sheaths in roots and shoots are covered or
impregnated by cutins and suberins.
 Cutin & wax occur on plant surfaces and the wax contains
fatty acids of 16-18 carbons is responsible for the hydrophobic
characters of cuticle and to hinder evaporation particularly in
the xerophytes.
 Suberin, 20-30 carbon atoms of long fatty acids and
polyphenols , cork cells walls are generally tightly anchored to
the plasma membrane assuring total water insulation.
Suberization also alters permeability of the cell walls
.Complete suberization of the wall barks and corks prevents
the contact between the cells and the environment that
sometimes leads to eventual cell death.

5.  The formation of wall ingrowths increases plasma membrane
surface areas of transfer cells involved in membrane transport
of nutrients in plants. Construction of these ingrowths
provides intriguing and diverse examples of localized wall
deposition. Flange wall ingrowths resemble secondary wall
thickenings of tracheary elements in morphology and probable
mechanisms of deposition. By contrast, reticulate wall
ingrowths, deposited as discrete papillate projections, branch
and fuse to create a fenestrated wall labyrinth representing a
novel form of localized wall deposition. Papillate wall
ingrowths are initiated as patches of disorganized cellulosic
material and are compositionally similar to primary walls,
except for a surrounding layer of callose and enhanced levels
of arabinogalactan proteins at the ingrowth /membrane
interface..

6.  How this unusual form of localized wall deposition is
constructed is unknown but may involve constraining
cellulose-synthesizing rosette complexes at their growing tips.
 Transfer cells are frequently located at sites of intensive
membrane transport of nutrients (Gunning and Pate 1969 ,
Offler et al. 2003 ). The unique feature of these anatomically
specialized cells is the presence of intricately invaginated wall
ingrowths, the contours of which are followed by plasma
membrane enriched in transporter proteins (Harrington et al.
1997 ). The increased surface area of plasma membrane, and
concentration of transporter proteins, facilitates elevated rates
of nutrient transport across the symplasmic–apoplasmic
interface (Patrick and Offler 1995 , Patrick 1997 ).

7.  The transfer cells first coined by Brain E.S. Gunning & John
Pate (1969) are characterized by
 i. enlarged lobed nucleus, numerous ER Cisternae, numerous
mitochondria and ribosome,
 Plasmodesmata connect transfer cells to other transfer cells
and to parenchyma cells,
 The wall ingrowths are formed just as intensive transport
begins, become first developed on the faces of the cell
presumed to be most active in solute transport
 It is apparently restricted to situations where adverse surface
to volume relationship exist between donor and receptor
compartments of the transport pathway
 The cell wall ingrowths of these cells provide intriguing
amnual diverse examples of localized wall depositions.

10.  The transfer cells functions relate to any of the four categories of
transmembrane flux as follows:
 Absorption of solute from the external environment like epidermis
of the submerged leaves,
 Secretion of solutes to the external medium like nectaries and other
glands,
 Absorption of solutes from the internal, extra cytoplasmic
compartment like vascular parenchyma, haustorial type connections,
embryo sac,
 Secretion of solutes into an extra cytoplasmic compartment like
tapetum of anther, pericycle of root nodule etc.
 Besides, the transfer cells form an anti-pathogenic barrier at the
symplastic discontinuties.As the transfer cells help in nutrient
transport, they are important in plant development and crop
productivity.